Epihalohydrin polymers are known to be susceptible to degradation reactions during aging and normal use of the vulcanizate. The principal degradation reaction is oxidation which may destroy the structural integrity of the polymer, as evidenced by the loss of molecular weight and the deterioration of physical properties to the point of mechanical failure. Such degradation may occur both before and after processing, for example, upon exposure to heat and light.
Degradation may also occur during the use of the finished article. For example, epihalohydrin polymers are employed extensively in the manufacture of hoses, gaskets, O-rings, and oil seals; all of these during use come in contact with various organic solvents, particularly, petroleum hydrocarbons. Such solvents, in combination with heat and weathering, cause articles composed of epihalohydrin polymers to deteriorate as evidenced by softening and deformation of the articles.
In the past, a number of various nitrogen-containing compounds have been used to slow down oxidative degradation of epihalohydrin polymers. For example, U.S. Pat. No, 3,239,486 discloses various metal salts of dialkyldithiocarbamates as antioxidants for use with epihalohydrin polymers. Metal salts of dialkyldithiocarbamates have also been used as antioxidative stabilizers in other polymeric materials, e.g., in polyethers (French Pat. No. 1,439,852), in cellular rubber (Chemical Abstracts, Vol. 28 (1951), Abstract 10646(b)) and in butadiene hydrocarbon elastomers (British Pat. No. 660,477). The nickel salt of di-n-butyldithiocarbamate has been utilized as an antioxidant for various epichlorohydrin vulcanization compositions (Encyclopedia of Polymer Science and Technology, Vol. 76, pp. 198-201; Chemical Abstracts, Vol. 76 (1972), Abstract 47154n; and Chemical Abstracts, Vol. 78, (1973), Abstract (137686h).
The prior art antioxidants, however, have imparted only limited overall aging resistance to epihalohydrin polymers with regard to degradation by oxygen, ozone, heat and ultraviolet light. Moreover, the prior art antioxidants often had to be supplemented with other stabilizers.